Hi GIZZ , i was able to figure this out on my own . So here are the steps :
1. If i understand correctly the first thing a ride would do when he buy a PaclTalk is pair his Mobile phone : By holding the Phone symbol button and then entering into Bluetooth pairing mode.
2. now in Cardo packtalk, ther are Two Bluetooth channels : Either to have two mobiles connection or 1 mobile & GPS navigation device or 1 mobile or anyother Sena Bluetooth
3. this is what you need to do for connecting the second Bluetooth device ( Sena Bluetooth pack or any other Bluetooth device ) on Channel 2 : Turn on the Packtalk first , then after it turns on press and hold the On/off button for 4secs to enter Pairing mode while this is happening make sure the SENA bluetooth pack is also in self pairing mode. automatically you will hear Cardo saying SENA bluetooth conneted. now you have Channel 1 - Mobile and Channel 2- Sena bluetooth.
4. how to switch between these two channel : whenever you turn the SENA bluetooth on , automatically the Cardo will connect to the Channel 2 and your phone will get disconnected.
5. you can even toggle using CArdo : Hold Phone button for 5 sec for Mobile 1 as default or Hold phone button for 3 sec for SENA bluetooth as the default bluetooth channel . ( havent tried this or tested this step )
hope this clarifies. you can also look at some of my video on youtube : "Vikas 190kph"